Glass composition and method



`Ian. 16, 1968 A 5.5WA1N ET Al. 3,364,042

GLASS COMPOSITION AND METHOD Filed Dec. 20, 1965 2 Sheets-Sheet A. B. SWAiN ET Al- `Jan. 16, 1968 3,364,042

l GLASS COMPOSITION AND METHOD Filed Dec.

2 Sheets-Sheet 2 CHAMPAGNE GREEN GLASS PRODUCED BY FOREHEARTH TECHNIQUE *i 4OO 2O 40 60 8O 500 2O 40 60 8O GOO 2O 40 60 BO 700 VVAVELENGTH IN MILLIMICRONS United States Patent y. Filed lilac. Eil, 1li/65, Ser. N $14,797 9 ffllaims. (Cl. MGH-52) This invention relates to the manufacture of colored glass. More particularly, the invention relates to highly colorant enriched green frit glass batch compositions and to the vitreous compositions made therefrom. Also, the invention relates to a method of manufacturing green composite glasses using said green frit glass of the invention. One specific embodiment of the invention relates to the manufacture of a commercial colored glass known as champagne green.

ln conventional operations for producing colored glasses, one of the very substantial problems encountered is in changing a glass melting tank over from one color to another or from a colorless to a colored glass making operation.

The problem arises from the fact that, for example, the first color composition must be dumped and the tank reiilled with a second color composition. Usually the tank change is so scheduled as to permit product run-out over as large a portion of the transition as possible. However, there is an intermediate interval of one to three days duration wherein the prior color tails out and the new color begins, in which the glass composition is in transition, and as such must be dumped. This transition glass is offecolor. Considering the fact that glass melting tanks hold up to 10G tons of melt or more, it will be understood that ti e ransition caused by dumping is very expensive.

This, of course, brings to mind an ideal situation wher a colorless base glass composition `would be used in the tank and colorant as desired added at the forehearth to fulfill specific end color requirements. By so operating, the conditions of tiring of the tank and the feeding of batch ingredients into the tank would all become fixed factors. Careful adjustment and stabilization of tank conditions would lead to the production of high quality products. The tank conditions, once stabilized, would remain so and variables would be avoider Such a forehearth coloring method has important advantages over the tank method for producing colored glass, in which the colorant material is added to the base glass batch and introduced directly into the melting and refining tank. Thus, by the fort-:hearth method, as many colors can be produced simultaneously as there are forehearths associated with the melting furnace.

Further, in a given forehearth, a transition from one color to another can be made in a matter of one to three hours as contrasted to a matter of one to three days to change a tank from one color to another.

Also, if desired, both clear and colored glassware can be made simultaneously from the same melting tank, by using different forehcarths, and adding colorant frit glass to some, and running *he clear base glass through others.

In manufacturing the green glass by techniques of the present invention, it is desirable to achieve high pulls or production rates from a selected forehearth or forehearths utilizing the invention. This may be achieved up to 4Q tons er operating day under the one modification herein disclosed.

Further, smaller quantities of colorant materials are required by the forehearth coloring method than by the known melting tank practice Where the colorant is incorporated into the tank batch and melted with substantial losses of volatile colorant materials during the extended mclting and refining operation.

Additionally, the manufacture of dark champagnegreen glasses by conventional methods has presented serious economic problems because of ineflicient use of fuel. These clark glasses have an absorption band in the infrared range of the spectrum causing much of the radiant energy of the llames to be absorbed in the upper layer of molten glass. Since commercial melting furnaces are designed to accommodate a depth of several feet of molten glass, heat transmission is a serious problem. Since color less ilint glass has a high transmission characteristic in the near infrared region of the spectrum, the present invention permits a substantial reduction in the melting costs by permitting the dark green colorants to be added after the melting has been completed.

Colored glasses are important in the glass industry as a good color improves the appearance of the glass and of the articles or products packaged in glass containers and enhances their sale in a competitive market. Various colors and shades of colors are produced commercially and are known in the trade by various trade names, as for example, Georgia green, Emerald green and Champagne green.

ln developing a champagne green by the above method in which the colorant is added within the forehearth, considerable difficulty has been experienced owing to detrimental el'fect of any unreduccd CrOs that may be present.

Presently, the commercial optical standards for champaghe green are:

Dominant wavelength ma 560-564 Purity, percent 40-50 Brightness, percent 12-20 Percent CrgG 0.07-0.09 C103 None lsliO 0.06 C00 0.004

These colorants are standard inthe industry.

This combination of colorants is possible because all of the CrOs can be reduced to Cr203 under carefully controlled conditions in the melting furnace. It is known that rzCrg contributes the strong green coloration while any unreduced Cr03 produces an undesirable yellow cast. The function of the Ni() is to darken the green coloration resulting from the Crgg. The COO is added to mask the yellow cast that would result from any unreduced Cr03. This is because there is generally a very minute quantity of CrOS present in the final glass even though it cannot be detected by conventional analytical means.

When champagne green is prepared by the forehearth technique (i.e., adding a green colorant enriched frit to a colorless base glass in the forehearth of a conventional furnace) it is very diicult to prevent some the the Cr203 present in the frit from oxidizing to Cr03 upon interaction with the base glass during the forehearth addition. This requires that additional C00 be added to mask the yellow produced by this additional Cr03 formed during forehearth addition. When enough C00 is added to the frit to bring the composite glass coloration with the specied dominant Wavelength, the color purity falls below the specified range. ln other words, the glass becomes too dark. For this reason, champagne green cannot be prepared by the forehearth technique using the conventional combination of colorants. The cause of the partial oxidation from @203 to CrO3 during the forehearth addition is not completely understood, but it is suspected to be a result of the interaction of the @T203 in the frit glass with the lining and decolorizing agents in the base glass at the prevailing forehearth temperatures under the influence of the ambient oxidizing conditions. ln any event, we have found that the use of COO as a masking agent for yellow is entirely unsatisfactory for commercial production of champagne green glass by the forehearth addition technique.

Therefore, a substantial contribution to the art of colored glass manufacture would be provided by highly enriched colored frit glasses for addition to colorless base glasses to produce commercially acceptable champagne green which has not been done before; further, a contri- Abution to the art would be provided by a method for producing such composite green glass.

It is therefore an object of the present invention to provide a novel green colorant frit glass particularly adapted to produce a composite glass within the commercial specification of champagne green when admixed with substantially colorless base glasses.

Another object is to provide commercial acceptable cahmpagne green composite glasses that do not require the use of cobalt oxide as a colorant.

Another important object is to provide a method of adding the green frit glass to the bulk stream of a molten base glass while the molten glass is flowing through the forehearth of a conventional melting furnace.

Still another object is to provide green frit glass compositions that are capable of admixing with colorless soda-lime base glasses in the forehearth of a conventional furnace to form commercially acceptable champagne green glasses so as to permit pull rates of up to 40 tons of nished glass per operating day.

In attaining the objects of this invention, one feature resides in the preparation of a frit glass containing in addition to the ordinary glass forming oxides, suflicient Cr2O3, CuO and NiO in proper combination to produce champagne green when admixed with a substantially colorless soda-lime base glass. The frit glass also contains sutiicient alkali oxides and other fluxes such as boric oxide to facilitate the dissolution of Cr203.

Another feature resides in admixing the aforesaid frit under proper conditions of agitation, in a forehearth of a commercial glass melting furnace, with an essentially colorless soda-lime base glass composition to produce the desired champagne green coloration.

The above and other objects, features and advantages of the present invention will become apparent to those skilled in the art upon reading the detailed description contained herein.

The specific problem presented to the art was to develop a colored frit glass that would yield a composite glass within the color specifications of champagne green when admixed with a soda-lirne base glass. initial experimentation demonstrated that a colored composite glass within the specifications of champagne green could not be produced by the forehearth technique utilizing the standard industrial colorants (Cr2O3, NiO and COO) in the frit glass. We found that during the forehearth addition of the frit glass to the base glass, part of the Cr2O3 was oxidized to CrO3 under the normal conditions of oxidation existing in the forehearth. When sufhcient C was added to neutralize the yellow cast produced by the CrO3, the color purity was lowered below the commercial speciiication. Rather than remove the ambient air from the forehearth and replace it with a neutral or reducing atmosphere, the problem was approached from a standpoint of finding a colorant to replace the C00 as a toning agent for the green resulting from the Cr2O3 while at the same time masking the undesirable yellow color resulting from any CrO3 that would be formed under the oxidizing forehearth conditions. It is important that this colorant cost no more than the CoO it would replace. We have discovered that a specified range of copper oxide as a replacement for the cobalt oxide in the frit glass would serve to give the resulting composite glass the proper green cast while at the same time masking the yellow color that inevitably forms during the forehearth addition under the ambient oxidizing conditions. In addition, the composite glass was unexpectedly found to be within the commercial specifications of champagne green from a color purity standpoint. The problem then was solved by replacing the cobalt oxide with a critical amount of copper oxide. The following description demonstrates in detail how the present invention can be practiced.

FEGURE 1 is a longitudinal sectional elevation of a preferred form of apparatus for use in practicing our invention.

The `base glass is melted and rened in the furnace tank lli. The molten glass lll flows through the furnace outlet 12 into the channel provided by the forehearth f3. The forehearth is provided at its forward end with an outlet 14 or other means for the discharge of the glass which may be under the control of plunger l5. The plunger may be operated to control the volume of glass passing through the outlet ld either by adjustment with respect to the outlet to control the flow therethrough, or by reciprocation thereover to discharge gobs of glass therethrough.

The green frit glass is fed to the surface of the glass in the forehearth channel from a feeder tank (not shown) through the discharge spout t7. Discharge blocks lfd, built into the upper wall or roof of the forehearth 19, are formed with vertical channels in register with the spout f7 through which the frit fall by gravity into the forehearth. The frit which is in powdered or granulated form is spread over the surface of the flowing glass. The frit falls on the glass directly over a darn 2G of Zac or other refractory material. The darn serves to produce a comparatively rapid local surface flow of the glass which aids in adrnixing the frit and base glass.

The forehearth comprises a section or chamber 22, through which the frit is carried and in which it is melted. The temperature in this section must be at least as high as the melting temperature of the frit and is usually maintained about Z200-2300o F.

In the well section 2S, the temperature is generally lowered approximately F. by the water cooled stirring members 2o and from this point on the glass it is gradually cooled to an average operating temperature at outlet le of about 207()o F. Means for effecting a thorough mixing of the melted frit with the base glass include a rst set of stirrers 24, bubblers 25, a second set of stirrers 2d and a third set of stirrers 27. The forehearth is formed with a well 28 and a deep well skimmer 29 extending downward within the well.

In another form, the frit may be added in the molten state. lt is therefore contemplated herein that the term frit may include either form of the colorant glass material.

The amount of frit entering the forehearth is usually only a small fraction of the amount of base glass flowing from tank .110, the proportion depending upon the composition of the frit, the intensity of the color desired in the end product, or other variable factors. ln general, the :amount of frit added usually varies from about 1% to about 5% by weight based on the amount of base glass.

The above described apparatus is only exemplary of several forms of apparatus which may be used in practicing the invention, and illustrates, rather schematically, the adoption of the method to existing forehearth constructions. For additional features of a suitable apparatus for mixing colorants in the glass furnace forehearth see U.S. Patent No. 3,057,175, to R. R. Rough and A. B. Swain, lr., issued on Oct. 9, 1962.

:i THE FRIT GLASS OF INVENTION AND METHOD OF PREPARATION TABLE L BATCII DATA FOR FRIT GLASS (IN POUNDS) Component Example Example Example Operable I II III Range Sand 2, OOG 2, 000 2, (100 2, 000 soda. Ash 1, 275 1, non 1,12 i, ooo-1, 275 Dehydrated Boraic 2 175 235 175- 270 Potassium Dichromate 198 124 174 124-1S8 Black Nickel Oxide 131 82 115 82-131 Black Copper Oxide 89 56 78 56-89 TABLE II.COMPOSITIONAL DATA FOR FRIT GLASS OF TABLE I IN PERCENT BY WEIGHT TABLE III.PREFERRED RANGE OF COLORAN'IS IN THE FRIT GLASS Colorant: Preferred range percent Cr2O3 2.3-2.7 CrO3 1 0-0.002 NiO 2.7-3.2 CuO 1.8-2.2

1 S11-Ould be as 10W as conditions permit.

Example 1 In one specific embodiment of the present invention, the batch ingredients listed in the corresponding column of Table I,'are tired in a frit furnace at a melting temperature of about 2750" F. To achieve the desired chromium concentration, all of the chromium is introduced as potassium dichromate. Hexavalent chromium is used because it is much more soluble in the alkaline soda-limeflint system. The presence of the sodium oxide and boric oxide in the frit enhances the ychromium dissolution. After complete dissolution, the Cr+6 is essentially reduced to Crt3 through interaction with the nickel oxide, copper oxide and other oxidizable material present in the batch under conditions of about O-1/2% excess oxygen in the melting chamber. The molten colorant glass is suitably converted to powdered frit by feeding as a stream from the outlet of the melting furnace and chilling rapidly. The chilling is effected by liowing the molten stream through water cooled rolls and then into a body of Water so that the glass breaks up into granular frit form. If desired, the granular glass frit can then be further reduced in particle size by grinding. We have found the powdered frit glass particles in the range of -8-l-30 mesh size are satisfactory for the purposes of this invention.

As an alternative method the frit may be melted and directly fed into the forehearth as the molten colorant frit glass.

In any event, the theoretical composition of the frit glass based on the above mentioned batch charge is listed in the corresponding column of Table II. The preferred range of colorants is set forth in Table III. The preferred values are slightly less than the theoretical values because of the slight Vaporization loss of colorant oxides during the frit melting operation. Therefore, the theoretical batch values are intentionally higher to allow for this slight vaporization loss on melting. It should be emphasized that it is desirable to have substantially all of the chromium in the frit glass and subsequently in the finished composite glass, present as Cr203 while the CIOS is held to a minimum.

Example II The corresponding frit glass of Table I is prepared according to the method of Example I. Composition data is set forth in Table II and Table III.

Example III The corresponding frit glass of Table I is prepared according to the method of Example I. Compositional data is set forth in Table II and Table III.

Before describing the manner in which frits of this invention are incorporated into colorless base glasses to produce champagne green composite glasses, a description of suitable base glasses and Idesired composite glass optical properties will be provided to serve as .an appropriate background upon which the invention can be superimposed.

Base glasses that can be used in practicing the present invention may have an actual analysis of Oxides encompassed within the ranges set out below. Generally, it will be found that giasscs falling within these ranges are sodalime-ilint glasses commonly used in the manufacture of colorless containers.

RANGE OF 'OXIDES IN BASE GLASS COMPOSITIONS Constituent: Percent by Weight SiOZ 60-75 A1203 (I3-10 Cao-i-MgO 6-15 NazO 12-18 H2O 0-5 BaO 0-5 Decolorizeri Trace *Any compatible decolorizer can be used. The function here is to mask the color produced by any iron that may be present as an impurity in the batch material. We have found that selenium in the rango of 0.000250.00035% is effective.

TABLE IIL-SPECIFIC COMPOSITION `OF A SUITABLE BASE GLASS Constituent: Percent by Weight SiO2 72.17 A1203 1.69 F6293 CaO 12.39 Mg() 0. 15 Naz() 13.25 K2@ 0.36 Selenium 0.00025-0-00035 The conditions and procedures for making the above base glass is lconventional and such condition are -Well known to those skilled in the art as exemplified in Table IX B-II on pages 245 of Handbook of Glass Manufacture by Tooley, Ogden Publishing Company, New York, N.Y., 1953.

In accordance with the broad principles of the present invention, tbe frit glasses of the invention can be added to substantially any oxidized glass. Accordingly, the exemplary soda-lime-ilint glass is suggested as applicable for commercial container production.

DESCRIPTION OF OPTICAL PROPERTIES The optical properties hereinafter set forth are CIE. colorirnetric values based upon the I.C.I. Chromaticity Diagram. CIE. refers to the First International Commission ot' Illumination and the diagram from which the values are taken defines color in terms of mixtures of theoretical color lights. The CIE. system makes possible the exact specication oi' colors by means of a color map. The CIE. system of color notation specifies the color of glasses in terms of brightness, purity and dominant wavelength.

Brightness which is usually expressed in terms of percentage, is the amount of visual response to a normal observer to the radiation emergent from a transparent object relative to the response in this observer to the radiation incident upon this object. Thus, brightness may be briefly termed the lightness of color of an object.

Purity which is also normally expressed in terms of percentage is a measure of the monochromaticness oi a color with monochromatic light having a purity of 100%. By diluting the monochromatic radiation with white light made up of all wavelengths, we thereby dilute the color and reduce purity.

Dominant Wavelength usually expressed in millimicrons (mp), is the wavelength of monochromatic light appearing to the eye to have the same hue as the mixed light actually encountered. These concepts will be hereinafter discussed in relation to the iinished composite glass.

In the production of glass containers7 a base glass is prepared in melting tanks of several hundred ton capacity. The batch constituents are added and proceed through the tank under melting and refining conditions. The glass is issued out of the lining end of the melting tank by being run through one or a plurality of orehearths which are provided in connection with the tank to feed the forming machines.

Generally, the colorless base glass issues from the melting tank into the forehearth at a temperature of about 2300 The frits made in accordance with the present invention are well adapted for addition to the base glass at such temperature conditions in finely divided form as from -S to +30 mesh size. stirring means and mixing bafiies known in the art are used to produce homogeneous admixtures of the rit into the colorless base glass to produce a uniformly, highly colored composite Ulass. A specic type of fore-hearth equipped with stirring is set forth in aforesaid FIG. l.

Example IV To produce dark green composite glass within the conrnecial specications of champagne green characteristic, the frit of Example Ill was added to the orehearth of a furnace producing the base glass listed in Table IV at the rate of about 55 lb. of frit glass per ton of base glass. ln practice, the amount of frit glass desirably ranges from about 1% to about 5% of the amount of base glass tlowing through the forehearth. The mixing was acomplished in an apparatus similar to that shown in FIG. l. The frit was at ambient temperature and the base glass was about 2300 F. The green composite glass was then formed into glass containers by conventional forming equipment.

The composite glass so produced had the following characteristics:

Preferred Range l Dominant Wavelength 562. 34 560-564 Purity, percent 44. 57 40-50 Brightness, percent 13. 24 12-20 Dominant wavelength 560.0 Purity, percent 47.2 BrigAness, percent 12.05

This comparison clearly demonstrates that we have developed a new composition that exhibits the same optical properties `as the standard champagne green composition.

The following table contains the actual composition of TABLE V Preferred Rango for Composition of In veution Frit Glass of Ex. HI and Base Glass of Table IV Conventional Champagne Green Composition Constituent of Finished Glass 1 As low as batch material permit. 2 As low as possible.

It is evident from the foregoing that the present invention provides a new glass composition having optical properties within the commercial specications of champagne green; a method of preparing said glass composition by the orehearth addition technique and a novel frit glass composition for use in said forehearth technique.

While the preferred embodiments have been described above in detail, it Will be understood that numerous modications might be resorted to without departing from the spirit and scope of the invention as defined in the following claims.

We claim:

1. ln a method of making a champagne green soda-lime glass, the steps of preparing a molten colorless soda-lime base glass, flowing the molten base glass through a forehearth, adding to the molten base glass in the forehearth a highly enriched colorant frit consisting essentially of soda-lime iint glass composition containing the following colorants:

Percent Total chromium as Cr203 2.1-3.1 Cu() 1.8-2.7 Ni@ 2.6-3.8

and forming a composite champagne green glass, the amount of frit glass added ranging from 1% to 5% by weight of the molten base glass.

2. In a method of making a colored glass composition, the steps of preparing a substantially colorless molten base glass having the following composition:

Oxide: Percent range SiOz 60-7 5 A1203 0.3-10 CaO-l-MgO 6-15 NaZO 12-1 8 K2() 0-5 BaO 0-5 Decolorizer Trace and adding to said molten glass a highly colored frit as dened in claim 1 and prepared from a batch of the following proportions by weight:

Ingredients: Parts Sand 2000 Soda ash G-1275 Dehydrated borax -270 Potassium dichromate 124498 Black nickel oxide 82-131 Black copper oxide 56-89 the amount of frit added being suicient to yield a nal colored glass composition containing colorants as follows:

Oxide: Percent range Cr203 0.005-0.062 CuO 0.05-0.10 NiO 0.06-0.08

and said nal glass ycomposition having C.I.E. colorimetric values for millimeter thickness of about 12-20% brightness, 40-50% purity and 560-564 millimicrons Idominant wavelength.

3. A rit composition consisting essentially of a sodalime int glass which is highly colorant enriched and which consists essentially of the following ingredients in the indicated percentage by weight:

Ingredient: Percent by weight Si02 55-67 A1203 0-1 Fe203 (impurity) 0-1 203 2-7 N320 -25 K 0-5 Total Cr as Cr203 2.1-3.1 N10 2.6-3.8 Cu0 1.8-2.7

4. The frit glass as described in claim 3, wherein the specific range of colorants is:

Percent Cf203 Cr03 0-0.002 Ni0 2.7-3.2 Cu0 1.8-2.2

5. The yrit glass as described in claim 3, wherein the specific composition is:

Percent Si02 61.9 A1202 0.15 B203 5.06 Na20 22.45 K20 1.73 Total Cr as Cr202 2.80 N10 3.50 C110 2.43

6. The frit glass as described in claim 3, wherein the specic composition is:

Percent SiO2 66.51 A1203 0.16 B202 4.05

Percent K20 1.36 Total Cr as Cr203 2.14 Ni0 2.69 Cu0 1.87

7. The frit glass as described in claim 3, wherein the specic composition is:

Percent Si02 58.71 A1203 0.14 B203 5.51 Na20 24.27 K20 1.90 Total Cr as Cr203 3.02 NiO 3.79 CuO 2.63

8. A green soda-lime glass composition consisting es sentially of:

Percent Si02 60-75 A1202 0.3-10 CaO, Mg0 6-15 Na20 12-18 K20 0-5 Total Cr as Cr203 0.05-0.062 CuO 0.05-0.10 Ni0 0.06-0.08

9. A glass composition as described in claim 8, wherein the specic composition is:

HELEN M. MCCARTHY, Primary Examiner. 

1. IN A METHOD OF MAKING A CHAMPAGNE GREEN SODA-LIME GLASS, THE STEPS OF PREPARING A MOLTEN COLORLESS SODA-LIME BASE GLASS, FLOWING THE MOLTEN BASE GLASS THROUGH A FOREHEARTH, ADDING TO THE MOLETEN BASE GLASS IN THE FOREHEARTH A HIGHLY ENRICHED COLORANT FRIT CONSISTING ESSENTIALLY OF SODA-LIME FLINT GLASS COMPOSITION CONTAINING THE FOLLOWING COLORANTS: 